Various control methodology and systems have been employed in conjunction with internal combustion engines so as to improve their performance, particularly in the areas of fuel economy and exhaust emission control. One of the more effective types of controls is a "feedback" control. With this type of control, a basic air/fuel ratio is set for the engine for given engine running parameters. An adjustment to this basic ratio is made, if necessary, based upon data from a sensor with senses the air/fuel ratio in the combustion chamber.
Normally, the type of sensor employed for this feedback control is an oxygen (O.sub.2) sensor. By determining the amount of oxygen in the exhaust gases from the combustion chamber, it is possible to fairly accurately measure the actual fuel ratio that was delivered to the combustion chamber. Most commonly, the sensor is arranged to sample the exhaust gasses after combustion, such as they pass through an exhaust passage leading from a combustion chamber.
The system operates on a feedback-control principle, continuously making corrections to accommodate deviations from the desired ratio. Adjustments are made in stepped intervals until the sensor output goes to the opposite sense from its previous signal. For example, if the mixture was running too rich, then adjustments are made in the lean direction until the mixture strength is sensed to be lean. Adjustments are then made in the opposite or rich direction in order to try to maintain the desired ratio.
For these systems to work properly, the data received from the sensor must be accurate. This requires that the sensor, in turn, sense a gas sample which is indicative of the true conditions with the combustion chamber. Achieving this goal in the outboard motor setting is difficult. Because of the size of the outboard motor, the exhaust system associated therewith is quite short. To provide reduce the temperature of the exhaust system and to achieve noise reduction, portions of the exhaust system are typically cooled. This cooling changes the characteristics of the exhaust therein.
In addition, the sensor must be mounted in a portion of the exhaust system which is accessible, and in the case of the outboard motor, still permits the exhaust system to fit within the small cowling of the motor and which is not in a location which exposes the sensor to water.
In accordance with the present invention there is a control system for an outboard motor, the control system including a sensor adapted to provide accurate sampling of exhaust gases to provide accurate feedback data.